1. Field of the Invention
The disclosures herein generally relate to an image forming apparatus.
2. Description of the Related Art
Some image forming apparatuses, including a printer, a copy machine, a plotter or a multifunction machine, may use a long rolled continuous print medium (hereinafter, referred to as a “roll of paper”).
In this kind of image forming apparatus, a load in a direction opposite to the medium conveyance direction of the roll of paper (a back tension) is applied in order to avoid wrinkling or twisting caused by skewed conveyance in which the roll of paper is conveyed in a skewed manner.
Conventionally, for example, a sophisticated method of correcting the skewed conveyance is known in which a torque limiter is included in a spool that supports the roll of paper in a rotationally free manner so that a rotational load is applied when rolling out the roll of paper, and in which a conveyance power changeable unit made of an electromagnetic clutch, which can change the conveyance power of the roll of paper, is included so that the back tension is controlled by setting a voltage applied for the electromagnetic clutch in accordance with a detected width of the roll of paper (refer to Patent Document 1).
Also, a method of variably controlling a back tension applied to the roll of paper is known in which a powder clutch engaged with a flange of the roll of paper is included for applying the back tension and in which an amount of electric power that is applied to the powder clutch is controlled in accordance with an output from a remaining amount of roll of paper detecting unit (refer to Patent Document 2).
In a configuration using an electromagnetic clutch or a powder clutch for changing the strength of the back tension, however, there is a problem that the configuration or the control becomes complicated and the cost becomes high.
[Patent Document 1] Japanese Patent Application Publication No. 2009-256061
[Patent Document 2] Japanese Patent Application Publication No. H09-164737